This invention is generally directed to processes for surface treatment of silica containing materials. In embodiments, the present invention relates to the surface treatment of silica surfaces with a coupling agent such as a silane. Treatment of the silica surface results in desirable surface properties that are different or dissimilar from that of the original silica surface. Specific surface properties achieved with the processes of the present invention include enhanced hydrophobicity, reduced surface energy, surface charging ability, improved wear resistance, friction coefficient reduction, enhanced affinity for specific gases, solids or liquids, and enhanced specificity of catalytic activity. In other specific embodiments, the present invention is related to toner and developer compositions, and more specifically, the present invention relates to toners containing surface treated silica particles. In process embodiments, the surface treated silica or metal oxides containing silica are prepared by a two step process comprising treating silicon dioxide, such as fumed silica, glass and related metal oxides containing silica, with an amine, and then with a coupling component, such as a silane. In specific process embodiments, micron or submicron silicon dioxide particles and metal oxide powders containing silica, such as a fumed silica, are treated by the two step process to obtain silane surface treated particulate materials. More specifically, silicon dioxide charge control additives that assist in enabling negatively and positively charged toner particles can be prepared by treating, for example, hydrophilic AEROSIL.RTM. A380 particles with a trialkyl amine like triethylamine, followed by reacting the intermediate product obtained with a silane coupling agent. Normally, metal oxides, such as many of the prior art silicon dioxides when incorporated into toners, provide or assist in providing a negative charge to the toner. The surface treated silica particles prepared by processes of the present invention when selected for toners may provide or assist in providing either positive and negative charge to the toner.
The surface treated metal oxide and silica particles, and toner compositions in embodiments of this invention may generally be prepared as described herein, and such processes comprise further aspects of the present invention. In embodiments of the present invention, the toner compositions are comprised of resin particles, pigment particles, and charge and performance enhancing additive surface treated metal oxide and or silica particles obtained with the processes of the present invention. One embodiment of the present invention relates to toner compositions comprised of a polymer resin or polyblend mixture, reference U.S. Pat. No. 4,556,624, the disclosure of which is totally incorporated herein by reference, of a first crosslinked polymer, a second polymer, pigment such as carbon black, a wax component, and a metal oxide, such as a surface treated silica charge enhancing additive obtained with the processes of the present invention, and optional surface additives such as silicas, metal salts, metal salts of fatty acids, or mixtures thereof. The developer compositions of the present invention are comprised of the toners illustrated herein and carrier particles. The carrier particles in embodiments of the present invention are comprised of a core free of a coating or with a polymeric coating, including, for example, a coating thereover generated from a mixture of polymers that are not in close proximity thereto in the triboelectric series, reference U.S. Pat. Nos. 4,935,326 and 4,937,166, the disclosures of which are totally incorporated herein by reference. Developer compositions comprised of the aforementioned toner and carrier particles are useful in electrostatographic or electrophotographic imaging and printing systems, especially xerographic imaging processes, including high speed processes, that is those generating from about 75 to about 125 copies per minute. Additionally, in embodiments, developer compositions comprised of the toners of the present invention and carrier particles of the aforementioned issued U.S. Patents are useful in imaging methods wherein relatively constant conductivity parameters are desired. Furthermore, in the aforementioned imaging processes the triboelectric charge on the carrier particles can be preselected depending, for example, on the polymer composition applied to the carrier core.
Advantages associated with the toners and developers of the present invention in embodiments thereof include desirable toner triboelectric charging characteristics, excellent toner flow properties, excellent toner admix characteristics, excellent color developer formulations for process color and transparency applications, stable performance for extended time periods exceeding, for example, 500,000 imaging test cycles in a xerographic imaging test fixture including those as illustrated in U.S. Pat. Nos. 4,394,429 and 4,368,970, the disclosures of which are totally incorporated herein by reference, the capability to vary the triboelectric charge on the carrier independent of the conductivity thereof; varying the conductivity on the carrier independent of the triboelectric charge thereof; use of the developer in imaging processes wherein a release fluid such as silicone oil is present; use of the developer in imaging processes wherein a minimum amount, or no release fluid, such as silicone oil is present; selection of the developer for electrophotographic, especially xerographic, heated fuser and pressure systems wherein the fuser roll coating is a silicone, reference for example the commercially available Xerox Corporation 1075.RTM. and 1090.RTM. imaging apparatuses; and the like.
Other advantages include providing a convenient and economic process for generating surface treated silica particles; toners and developers thereof; enhanced toner flow; enhanced toner transfer efficiency; and colorless particles for use in multicolor xerography.
Toners with charge additives, including those that impart a positive charge, or negative charge to the toner are known generally. Toner compositions with crosslinked resins and second resins, together with waxes and charge enhancing additives are disclosed, for example, in U.S. Pat. No. 4,556,624, the disclosure of which is totally incorporated herein by reference, and some of the prior art references mentioned thereon, and cited against the '624 patent. More specifically for enhancing the positive charging characteristics of toner compositions there can be incorporated in the toner charge enhancing additives, inclusive of alkyl pyridinium halides, reference U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference, organic sulfate or sulfonate compositions, reference U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference; distearyl dimethyl ammonium sulfate, reference U.S. Pat. Nos. 4,560,635 and 4,937,157, the disclosures of which are totally incorporated herein by reference; and other similar known charge enhancing additives including other quaternary ammonium salts. These additives are usually incorporated into the toner in an amount of from about 0.1 percent by weight to about 10, and preferably in an amount of from about 0.1 to about 5, and more preferably from about 0.3 to about 1.0 percent by weight. The triboelectric charge of the toner as determined, for example, by the known Faraday Cage process, or a charge spectrograph is from about positive or negative 5 to about 120, and preferably from about 10 to about 60 microcoulombs per gram. Toners with negative charge additives, such as aluminum complexes, reference U.S. Pat. No. 4,845,003 are also known. Moreover, other toner formulations containing metal oxides, such as tin oxides are generally known and function as a positive charge additive.
The following prior art, the disclosures of which are incorporated by reference in their entirety, are also mentioned:
Smith, U.S. Pat. No. 3,635,743 issued Jan. 18, 1972, discloses a reinforcing silica filler made by first treating a fine particle silica with ammonia and then treating the filler with, for example, hexamethyldisilazane and related compounds. The process of making reinforcing silica powder requires a finely divided silica having at least 0.2 weight percent absorbed water (col. 1, line 66 to 71).
A publication by Leyden et al., J. Am. Chem. Soc., 1987, 109, 7141-7145, discloses amine catalyzed reactions of alkoxysilanes with silica wherein the amine and the alkoxysilane are both added at the same time in a solution to the silica. Reactions with methoxymethylsilanes when ammonia is present provides a monolayer or greater surface coverage and when ammonia is absent a 12 fold decrease in silane surface coverage is obtained.
A reference of general relevance is "The Chemistry of Silica," Iler R. K., Wiley, 1979.
A disadvantage in many prior art methods, for example, using solution coating methods, for preparing metal oxide particulate charge and flow additives is that solvents, particularly hydrogen bonding solvents, often cause irreversible agglomeration of submicron oxide particles thereby destroying the submicron particle dispersibility and flow improving capacity on toner surfaces. Optimal modification of toner charging properties usually requires high submicron particle dispersibility.
Other disadvantages of prior art methods for preparing silane surface treated metal oxides include: employing anhydrous, gas phase and high temperature conditions and therefore limits suitable silanes that are thermally stable that can be selected; the silane is not entirely chemically bonded to the metal oxide surface leading to variability in performance characteristics of the treated particles in various applications; the silane may polymerize prior to reacting with the particle surface resulting in lower yields; particle agglomeration; inhibition of bonding of the coupling agent to reactive surface groups, such as surface hydroxyl groups, resulting in residual unreactive groups with undesirable properties; contaminated product; and high processing costs.
Thus, there remains a need for a metal oxide surface treatment process that limits undesirable non-surface coupling agent polymerization. Further there is need for a surface treatment process where the coupling agent is completely or nearly completely chemically bonded to the surface. Furthermore, there is a need to provide more robust coatings, as provided when the coupling agent is covalently bound to the metal oxide surface.
There also remains a need for black or colored toners wherein toner flow and charging properties may be readily attained by the addition of surface treated metal oxide or silica particles of the present invention. Furthermore, there is a need for a silica particle surface treatment processes wherein the synthetic yields are high, such as from about 70 percent to nearly quantitative and without resorting to excessive isolation and purification procedures and which surface treatment processes provide a means for selectively modifying metal oxide and silica surfaces with varying amounts and various types of organosilane compounds to achieve engineered metal oxide surfaces and particle surfaces. In addition to the above, there is also a need for black and colored toners that are of excellent image resolution, non-smearing and of excellent triboelectric charging characteristics. In addition, there is a need for toners containing surface treated silica particles which possess triboelectric charge stability under varying ambient humidity conditions. Furthermore, there is a need for toners containing surface treated silica particles which possess excellent flow properties. In addition, there is a need for black or colored toners with low fusing temperatures, of from about 110.degree. C. to about 150.degree. C. as determined by known minimum fix temperature techniques and glass transition temperature measurements, of high gloss properties such as from about 50 gloss units to about 85 gloss units as measured by a VWR 75.degree. gloss meter, of high projection efficiency, such as from about 75 percent efficiency to about 95 percent efficiency or more, and, in addition, result in developed images with minimal or no paper curl.